(1) Field of the Invention
The present invention generally relates to a semiconductor device and, more particularly, to a semiconductor device in which a semiconductor chip is bonded to lead portions and encapsulated in plastic, the semiconductor chip having a bottom surface covered with the plastic, which plastic is likely to crack due to heat stresses.
(2) Description of the Prior Art
A semiconductor device in which a semiconductor chip is bonded to lead portions and enclosed in a plastic package is known. Before the plastic package is molded to enclose the semiconductor chip, the semiconductor chip is bonded onto a die pad, the semiconductor chip having a bottom surface covered with the die pad. When the semiconductor device of this type is bonded onto a printed circuit board, a portion of the plastic package on the bottom surface of the semiconductor chip is affected by heat. The portion of the plastic package on the bottom surface of the semiconductor chip is likely to crack due to heat stresses between the plastic package and corners of the die pad. To increase the reliability of the semiconductor device as a manufactured product, it is desirable that the plastic package does not crack if the heat stresses occur.
FIG. 1 shows a conventional semiconductor device in which a semiconductor chip is bonded to lead portions and enclosed in a plastic package. In FIG. 1, the semiconductor device 1 has an epoxy resin package 2 and a semiconductor chip 3 enclosed in the epoxy package 2. A certain filler is added to the epoxy resin package 2 so as to increase the strength of the epoxy resin package 2.
In the semiconductor device 1, a bottom surface 3a of the semiconductor chip 3 is covered with a die pad, and the die pad adheres to the epoxy resin package 2. However, the adhesion between the epoxy resin package 2 and the die pad is not sufficiently firm.
The semiconductor device 1 is subjected to heat when it is bonded onto a printed circuit board, and especially a bottom portion of the epoxy resin package 2, covering corners of the die pad, is influenced by heat stresses. Moisture in the epoxy resin package 2 vaporizes in the heat. Since the volume of the vapor in the epoxy resin package 2 is much greater when the semiconductor device is subjected to heat than before it is heated, heat stresses between the semiconductor chip 3 and the die pad and heat stresses between the epoxy resin package 2 and the die pad are produced. The epoxy resin package 2 and the die pad at the corners are likely to be separated from each other. Cracks 4 in the bottom portion of the epoxy resin package 2 may be produced due to the heat stresses. If the epoxy resin package 2 cracks, the entry of humid air through the cracks into the epoxy resin package 2 will make the reliability of the semiconductor device 1 low, and will make the life of the semiconductor device 1 shorter.
Accordingly, it is a general object of the present invention to provide an improved semiconductor device in which the above described problems are eliminated.
Another, more specific object of the present invention is to provide a semiconductor device in which a semiconductor chip is bonded to lead portions and enclosed in a plastic package, adhesion between the semiconductor chip and the plastic package after the plastic package is molded around the semiconductor chip being increased to a level sufficient for preventing a portion of the plastic package on a bottom of the semiconductor chip from cracking due to heat stresses.
The above mentioned objects of the present invention are achieved by a semiconductor device which includes a semiconductor chip and a plastic package for enclosing the semiconductor chip in a plastic material through a molding process, the plastic package fully or partially covering a bottom surface of the semiconductor chip with the plastic material, wherein an ultraviolet cleaning process is performed for cleaning the bottom surface of the semiconductor chip prior to the molding process.
According to the present invention, it is possible to increase adhesion between the semiconductor chip and the plastic package after the molding process is performed, thereby preventing the plastic package from cracking due to heat stresses. The reliability of the semiconductor device thus manufactured can be increased, and the life of the semiconductor device can be made longer.